Problem: Which of these numbers is composite? ${19,\ 33,\ 37,\ 83,\ 89}$
Solution: A composite number is a number that has more than two factors (including 1 and itself). 19, 37, 83, and 89 each have only two factors. The factors of 33 are 1, 3, 11, and 33. Thus, 33 is the composite number.